Storing And Transporting Energy

ABSTRACT

Among other things, hydrogen is released from water at a first location using energy from a first energy source; the released hydrogen is stored in a metal hydride slurry; and the metal hydride slurry is transported to a second location remote from the first location.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority to U.S.application Ser. No. 12/820,737, filed on Jun. 22, 2010, which is adivisional of and claims benefit to U.S. application Ser. No.11/392,149, filed Mar. 29, 2006 entitled “Storing and TransportingEnergy”. The disclosure of the prior application is incorporated byreference in its entirety.

BACKGROUND

This description relates to storing and transporting energy.

Energy in the form of electricity can be stored in the form of hydrogen,for example, by applying the electricity to an electrolysis process todisassociate the hydrogen from oxygen in water. Energy in the form ofheat can also be stored in the form of hydrogen by using a thermalconversion process to dissociate the hydrogen from oxygen in water.

Hydrogen can be transported safely and easily by incorporating it into ametal hydride. Later, the hydrogen can be released by mixing water withthe metal hydride and used to provide energy, for example, to a car.

SUMMARY

In one aspect, methods are provided that include generating hydrogenusing electricity or heat, and combining the hydrogen with a pumpablefluid to form a pumpable hydrogen storage fluid. The pumpable hydrogenstorage fluid is not subject to significant hydrogen evolution at roomtemperature and pressure.

In one aspect, methods are provided that include releasing hydrogen fromwater at a first location using energy from a first energy source,storing the released hydrogen in a metal hydride slurry, andtransporting the metal hydride slurry to a second location remote fromthe first location.

In one aspect, systems are provided that include an electrolyzer toextract hydrogen from water using energy from a first energy source at afirst location and a charging device coupled to the electrolyzer. Thecharging device has a slurry inlet, a slurry outlet, and a heatingdevice capable of heating a slurry in the charging device to at leastabout 320° C.

In one aspect, systems are provided that include an electrolyzerincluding electrical terminals and a hydride slurry charging devicecoupled to the electrolyzer.

In one aspect, systems are provided that include a first device toproduce hydrogen using electricity from a first energy source, a metalhydride slurry charging device coupled to the first device, a metalhydride slurry storage vessel coupled to the metal hydride slurrycharging device, and a pump to pump a slurry from the metal hydrideslurry charging device to the metal hydride slurry storage vessel.

Implementations may include one or more of the following.

In some embodiments, the pumpable inert fluid comprises a reversiblehydride former. In some embodiments, the reversible hydride formerincludes a reversible metal hydride former, (e.g., magnesium) and/or areversible metal alloy hydride former.

In some embodiments, the methods further include releasing hydrogen fromthe metal hydride slurry to form hydrogen and a metal hydride slurrythat is at least partially depleted.

In some embodiments, the methods include transporting the partiallydepleted metal hydride slurry from the second location to the firstlocation, e.g., for recharging the partially depleted metal hydrideslurry. For example, the partially depleted metal hydride slurry can insome instances be recharged by releasing energy from water at the firstlocation using energy from the first energy source, and storing thereleased hydrogen in the depleted metal hydride slurry to form the metalhydride slurry. The metal hydride slurry can in some embodiments bedepleted and recharged for at least 50 cycles.

In some embodiments, the first energy source can include a renewableenergy source (e.g., wind, hydroelectric, geothermal, ocean power,solar, and/or combinations of these). The first energy source can beused in some embodiments to release hydrogen from water, and thehydrogen can be stored in a metal hydride slurry at the first location.In some embodiments, the metal hydride slurry can be transported via acarrier (e.g., a rail car, a truck, a tanker, a pipe, and anycombination of these) from the first location to a second location. Insome embodiments, the hydrogen that is released from the metal hydrideslurry (e.g., at the second location) can be utilized as an energysource (e.g., in a fuel cell). In this fashion, energy from the firstenergy source can be effectively stored and transported to a secondlocation. In some embodiments, the first location has a first energydemand, the second location has a second energy demand, and the firstenergy demand is lower than the second energy demand.

In some embodiments, the metal hydride slurry comprises magnesium,magnesium hydride, and mineral oil. In some embodiments, the metalhydride slurry further comprises a dispersant.

In some embodiments, the systems are capable of maintaining a pressurein the charging device of at least about 150 psia. In some embodiments,the charging device comprises a pump to pump a slurry from the chargingdevice through the slurry outlet, e.g., to a storage container coupledto the charging device slurry outlet. In some embodiments, the chargingdevice includes a regulator to maintain a temperature of a slurrycontained in the charging device at no more than about 350° C.

In some embodiments, the systems include a discharge device including aheating device capable of heating a hydride slurry contained in thedischarge device to at least about 370° C. In some embodiments, thedischarge device includes a hydrogen outlet through which hydrogenevolved from a hydride slurry can pass.

In some embodiments, the first device of the system includes anelectrolyzer.

In some embodiments, the systems include a pump coupled to the storagevessel to transfer a slurry from the metal hydride slurry storage vesselto a slurry carrier (e.g., a truck, a boat, a rail car, a pipe, or anycombination of these).

In some embodiments, the systems include a metal hydride slurrydischarge device that removes hydrogen from a metal hydride slurry.

In general, other aspects include the above features and aspects aloneand in other combinations, expressed as methods, apparatus, systems,program products, and in other ways.

Among the advantages of these and other features and aspects are one ormore of the following.

Energy can be stored in the hydrogen at a place where the energy isreadily available, for example, from wind and/or the sun, but the demandfor energy is relatively low, and transported to a place where energydemand is high.

Other features and advantages will be apparent from the description andfrom the claims.

DESCRIPTION

FIG. 1 is a schematic diagram of storing and transporting energy.

FIG. 2 is a schematic diagram of a metal hydride charging device.

FIG. 3 is a schematic diagram of a metal hydride discharging device.

FIG. 4 is a plot of temperature and pressure versus time for chargingand discharging a metal hydride slurry.

Generally, systems and methods are provided in which energy is storedand/or transported in the form of hydrogen. For example, energy in theform of hydrogen can be stored by incorporating the hydrogen into areversible metal hydride slurry, which is a slurry that includes acomponent (e.g., a metal or metal alloy) that can accept hydrogen atoms(can be hydrided) and can give up hydrogen atoms (can be dehydrided) ina reversible fashion, depending on the conditions (e.g., heat and/orpressure) to which the slurry is subject. Slurries that include areversibly hydridable component can generally be described as “charged,”in which a substantial amount (e.g., 80% or more) of the hydridablecomponent is hydrided; “depleted,” in which a substantial amount (e.g.,80% or more) of the hydridable component is not hydrided; or “partiallycharged,” in which the slurry contains both hydrided and non-hydridedcomponents, with the hydrided component being generally present in anamount between about 20% and 80% of the total amount of hydridablecomponent. Typically 85% to 95% of the amount of the hydridablecomponent will be hydrided when charged and 5% to 15% will be hydridedwhen depleted. In a worst acceptable case, likely at least 70% would behydrided when charged and 5% when depleted. In general, a “charged”slurry can include some level of hydridable component that is nothydrided, and a “depleted” slurry can include some level of hydridablecomponent that is hydrided. In determining whether a slurry isconsidered charged or depleted, commercial factors can be considered;for example, a slurry can be considered “charged” when it has enoughhydrided material to provide a desired amount of energy from thathydrogen when it is subject to hydrogen evolution. Factors such as thecost and time of hydriding the slurry, cost of transportation of theslurry to the site of hydrogen evolution, and the cost of alternativesources of energy at the site of hydrogen evolution can be considered indetermining when a slurry is charged.

In the example of storing and transporting of energy 10 shown in FIG. 1,energy available at a first location 12 (in this case, a windmill farmin Kansas) is stored in a safe, easily handled transportable medium (inthis case, hydrogen in a rechargeable metal hydride slurry) to a secondlocation (in this case, New York) where the energy is used, e.g., incars that are able to burn hydrogen as a fuel.

At a first location 12, wind causes rotors 19 of windmills 15 to spin,driving generators 17 to produce electricity. The electricity is carriedon cables 16 to electrical terminals 18 of an electrolyzer 20. Theelectrolyzer is part of an energy charging system 13 that also includesa charging device 30.

Using the electricity, the electrolyzer 20 separates water into hydrogengas 23 and oxygen gas 25. The water is provided from a source 21 througha pipe 22. The hydrogen gas 23 is passed through a hydrogen gas outlet24 and a pipe 26 into the charging device 30. The oxygen gas 25 isvented from the electrolyzer 20 through an oxygen gas outlet 28, whereit can be collected for further use or vented to the atmosphere.

In some examples, the electrolyzer 20 pumps the hydrogen gas 23 into thecharging device 30 under pressure (e.g., at least about 50 psia [poundsper square inch absolute]) and the contents of the charging device aremaintained under pressure. The pressure could be in a range of about 100psia or more, 150 psia or more, 200 psia or more, 250 psia or more, 500psia or more, 1000 psia or more, or 1500 psia or more. The pressurelevel is set based on the ability of the charging device to withstandpressure and handle the heat generated by the reaction. The reactionbetween the metal hydride and the hydrogen will produce heat and chargedmetal hydride. The reaction rate of the depleted metal hydride withhydrogen is typically faster with higher pressure. An optimal systemcould use a hydrogen pressure that maximizes the system production ratewhile minimizing the system cost. A higher production rate willtypically require a smaller and possibly less expensive charging device.On the other hand, a rapid reaction rate might produce so much heat thatthe heat removal system becomes costly. An optimal system could balancethe costs to yield a minimum cost design. One advantage of the metalhydride being in slurry form is that the slurry can be stirred to aid inheat transfer.

In some examples, not illustrated in FIG. 1, the hydrogen gas 23 iscollected in a hydrogen gas tank where it is pressurized before beingdelivered to the charging device 30. For example, if the cost ofpressurizing the hydrogen to a particular pressure is less than the costof using an electrolysis device that operates at that pressure, or ifthe hydrogen source is at a lower pressure than is required by thecharging device, a pressurized hydrogen tank can provide hydrogen at thenecessary pressure.

In addition to the hydrogen, the pressurized charging device 30 receivesa stream of depleted reversible metal hydride slurry 34. A depletedreversible metal hydride slurry can be a slurry that has not yet beenhydrided (e.g., a newly-formed slurry) and/or a slurry that has been atleast partially dehydrided. Each is discussed in greater detail below.The depleted reversible metal hydride slurry, sometimes simply called adepleted slurry, metal hydride slurry, or slurry, includes both metalhydride and elemental metal in a form that is able to accept additionalhydrogen to form metal hydride. The proportion of metal hydride toelemental metal in the slurry can be 1.2% or more by weight.

Other components can be included in the depleted metal hydride slurry,for example, a carrier liquid, such as an organic carrier, and/or adispersant for stabilizing the slurry, such as a triglyceride orpolyacrylic acid (˜1%) or oleic acid (˜0.125%). The depleted slurry isdrawn by a pump 40 through a pipe 42 from a depleted reversible metalhydride slurry source (for example, a depleted metal hydride slurrystorage device 46) and forced through a depleted metal hydride slurryinlet 31 into the charging device 30.

The slurry in the pressurized charging device 30 is then heated usingheating coils 36. When the slurry is heated, the metal hydride in theslurry is able to be further charged with hydrogen gas 23, whereby theamount of hydrogen in the form of a metal hydride in the metal hydrideslurry is increased. For magnesium hydride, the reaction rates are veryslow until the temperature of the hydride is above about 280° C., soheating the magnesium hydride to this temperature can speed up theinitial reaction. The rate then generally quickens, and the temperatureand/or pressure can be lowered to control the reaction rate. By thisprocess, the depleted metal hydride slurry becomes a charged metalhydride slurry 38, as described below. The temperature to which thepressurized slurry is heated for charging can be within a wide range,for example, in the range of from about 50° C. to about 350° C.,depending on the metal hydride used in the slurry. For magnesiumhydride, the charging range is from about 250° C. to about 400° C.(e.g., from about 260° C. to about 300° C.). The preferred temperaturerange will generally depend on the rate of reaction between the hydrogenand the depleted metal hydride.

Generally, the temperature and pressure for hydriding the slurry willdepend on each other, and will depend on the type of metal being used inthe slurry. For example, magnesium hydride requires relatively hightemperatures and pressures to hydride the slurry at an acceptable rate;the equilibrium temperature of magnesium hydride at 1 atmosphere is 279°C. Other metal hydrides can typically achieve similar reaction rates atlower temperatures and/or pressures.

After the charging, the charged reversible metal hydride slurry 38 iscooled, e.g., to room temperature. The cooled charged metal hydrideslurry 38 does not release a significant amount of hydrogen while itstemperature remains within a cool range, and is therefore safe to storeand/or transport. A “significant amount” of hydrogen is an amount largeenough to significantly affect the amount of energy available at thesite of hydrogen evolution or the cost-effectiveness of using the slurryas a source of energy, or enough to create storage and/or transportationdifficulties, for example, due to increases in pressure resulting formthe production of hydrogen. For example, in some embodiments, the cooledcharged metal hydride slurry releases no more than about 1% of its totalhydrogen (e.g., no more than about 10%, no more than about 1%, or nomore than about 0.1% of its total hydrogen). In some cases, it isbelieved that the amount of hydrogen release would be less (evenconsiderably less than) 0.1%. The available range of temperatures atwhich the charged metal hydride slurry does not release a significantamount of hydrogen depends on the metal hydride used in the slurry. Formagnesium hydride, the slurry will not produce significant amounts ofhydrogen at temperatures below about 200° C. (e.g., below about 100° C.,below about 80° C., below about 60° C. or below about 40° C.). Otherreversible hydrides typically must be kept cooler.

Once the slurry has been charged, a pump 48 pumps the charged slurry 38from a charged metal hydride slurry outlet 37 through a pipe 50 to acharged slurry storage device 52, where the charged metal hydride slurrycan be stored indefinitely. The charged slurry storage device 52 has anoutlet 56 to allow the slurry to be withdrawn by a pump 58 into a slurrycarrier 60, here a tanker truck. The slurry carrier 60 could be anythingcapable of moving a fluid over a distance, such as automotive vehicles,rail cars, ships, barges, and pipes or other conduits. The carrier couldbe trucks of the kind that are used to transport gasoline. The pump 58can be part of a service station that is dedicated to serving trucksfrom a single distributor or can be available to serve trucks ofmultiple distributors.

The slurry carrier 60 transports the charged metal hydride slurry 38,including the energy stored in the hydride in the form of hydrogen, fromthe first location 12 to the second location 62.

At the second location, a station for offloading the transported slurryincludes a pipe 76 through which a pump 73 withdraws the slurry from thetransporter and pumps it to a charged slurry storage tank 75. Whenhydrogen is needed, charged slurry is pumped by pump 74 from the chargedslurry storage tank 75 through pipe 77 to a slurry inlet 72 and into adischarge device 70.

The discharge device contains a heater 78 (e.g., a heating coil) forheating the slurry to a temperature at which the metal hydride of theslurry releases hydrogen. The heating temperature is dependent on thedischarge characteristics of the metal hydride in the slurry. Formagnesium hydride, the heating temperature is from about 250° C. toabout 400° C. (e.g., from about 290° C. to about 370° C. or from about320° C. and 360° C.). Other hydrides can have different temperatures atwhich they release hydrogen. Generally, the temperature will be leastabout 150° C. (e.g., at least about 80° C., at least about 100° C., atleast about 125° C., at least about 175° C., at least about 200° C., atleast about 225° C., at least about 250° C., at least about 275° C., atleast about 300° C., at least about 325° C., at least about 350° C., atleast about 375° C., or at least about 390° C.) and/or at most about400° C. (e.g., at most about 390° C., at most about 375° C., at mostabout 350° C., at most about 325° C., at most about 300° C., at mostabout 275° C., at most about 250° C., at most about 225° C., at mostabout 200° C., or at most about 175° C.).

The discharge device will typically operate at a pressure determined bythe discharge characteristics of the metal hydride and the systemeconomics. For magnesium hydride, the highest discharge rates occur witha pressure near atmospheric pressure or lower. However, hydrogencompressors typically cost less if the hydrogen is provided at apressure ranging from 30 psia to 100 psia. In this case, the dischargedevice may be operated in the range of 30 to 100 psia to reduce the costof the hydrogen compressor. The pressure range will typically beselected to minimize the cost of the system. For example, if thehydrogen is to be consumed by a fuel cell, the pressure required mayonly be 16 to 20 psia. In this case, the discharge device will likely beoperated at a pressure of 16 to 20 psia to eliminate the need for ahydrogen compressor.

The discharge device is designed to exclude air and water, specificallyoxygen and water. The charging device is also designed to exclude airand water as these materials can react with the metal hydride andprevent it from absorbing or desorbing hydrogen.

As the charged metal hydride slurry 38 is heated and the hydrogen gas 23is discharged, the slurry becomes a depleted metal hydride slurry 34 (ametal hydride slurry that includes less than a significant amount ofhydrogen, for example, because some of the hydrogen has evolved from theslurry or because the slurry has been newly formed and has not beenhydrided). The depleted reversible slurry is withdrawn by a pump 84through a gas outlet 80 into a slurry carrier 60 (which could be, forexample, the same trucks used to carry the charged slurry) for transportback to the first location 12 (or another recharging facility) forrecharging.

The hydrogen gas 23 that is discharged from the charged metal hydrideslurry 38 is vented through a gas outlet 80 and collected, e.g., bottledin a hydrogen bottle 90. The bottled hydrogen can be subsequently usedas a source of energy, effectively transporting the energy from, forexample, the wind farm in Kansas to, for example, New York, where theenergy demand is higher than in Kansas. The bottled hydrogen could beused, for example, to power fuel cells in a vehicle. For example, thehydrogen can be discharged from the bottle into a fuel cell in a vehicleat a service station, or the bottle itself can be placed in a vehicleand can be incrementally fed into a fuel cell in the vehicle. Thehydrogen can be bottled as a gas or as a liquid. In some cases, thehydrogen can be put to a use other than as an energy source. Forexample, the hydrogen can be used in laboratory work as a carrier gasfor a gas chromatograph, as a reactant in a chemical reaction requiringhydrogen, or as a welding gas, e.g., to replace acetylene.

In some embodiments, the rechargeable metal hydride slurry can be usedas an energy source for a vehicle directly, rather than as a source forbottled hydrogen. For example, the rechargeable metal hydride slurry canbe pumped directly into a vehicle, e.g., into a storage tank in avehicle. The vehicle can have a discharge device located within thevehicle, allowing for the evolution of hydrogen for use as a fuel sourcein the vehicle. In some embodiments, the vehicle could also have acharging device, such that the rechargeable metal hydride slurry can berecharged within the vehicle itself. Hydrogen from a hydrogen source canbe pumped into the charging device in the vehicle to hydride the slurry.

In some implementations, the reversible metal hydride slurry caninitially be formed at the first location 12, e.g., in the chargingdevice 30. For that purpose, an inert liquid (for example, mineral oil)105 can be withdrawn by a pump 104 from an inert liquid tank 100 throughan inert liquid pipe 102 and into the charging device 36. Also includedis a storage container 106 for storing a metal hydride former 107, forexample, an elemental metal in powdered form. The storage container 106is coupled to the charging device 30 through a conduit for transfer intothe charging device 30. Alternatively, one or both of the storagecontainer 106 and the inert liquid device 100 can be uncoupled to thecharging device; then the inert liquid 105 and/or the hydride former 107can be added to the charging device 30 by hand. Other slurry components,such as, e.g., a dispersant and/or a hydride catalyst, can be stored andadded to the charging device 30 to form the slurry. The hydride former107, inert liquid 105, and optional additional ingredients can becombined in the charging device 30 to form an initial depleted slurry34.

In some examples the reversible metal hydride slurry can initially beformed at another location and trucked to the first location 12 for use.

Although only one first location having one charging device and onesecond location having one discharge device are shown in FIG. 1, thefirst location may include multiple charging devices, the secondlocation may include multiple discharge devices, and there may bemultiple first locations and second locations forming a distributionnetwork for energy derived at some locations and used at otherlocations.

In some examples, the slurry generally includes a carrier liquid, suchas an organic carrier, a dispersant, such as a triglyceride, forstabilizing the slurry, and a reversible metal hydride and/or reversiblemetal hydride former (i.e., the metal and/or alloy of the metal hydridein elemental form) dispersed in the carrier liquid. The concentration ofthe hydride and/or hydride former in the slurry is typically in therange of 40 to 80 wt % (e.g., 50 to 70 wt % or 55-60 wt %). Theconcentration is generally dependent on the metal hydride selected foruse in the slurry. The use of denser metal hydrides will result inhigher metal hydride concentrations than will the use of less densemetal hydrides. Dense metal hydrides are metal hydrides having a densityof at least about 1 gm/mL, and include, for example, lanthanumpenta-nickel, while less dense metal hydrides have a density of no morethan about 1 gm/mL, and include, for example, lithium hydride. Magnesiumhydride slurries can have hydride concentrations of at least about 50 wt% (e.g., at least about 55 wt %, at least about 60 wt %, at least about65 wt %, at least about 70 wt %, or at least about 75 wt %), and/or atmost about 80 wt % (e.g., at most about 75 wt %, at most about 70 wt %,at most about 65 wt %, at most about 60 wt %, or at most about 55 wt %).Generally, higher percentages yield higher energy densities (i.e., theamount of energy that can be obtained from given volumes of slurry)while being generally more viscous and can require more force to pump,while lower percentages are typically less viscous, requiring less forceto pump, but yielding a lower energy density.

The slurry can be safely stored and transported, and the hydrogen may beeasily extracted for use as a fuel. The slurry is generally not highlyflammable or combustible and may be safely handled, stored, andtransported. The slurry is stable at normal environmental temperaturesand pressures, for example, such that hydrogen does not dissociate fromthe hydride and evolve. Because it is a liquid, the slurry can easily bepumped through conduits and into storage tanks, transportation devices,and/or charging and discharging devices.

The slurry includes a carrier liquid, e.g., an inert liquid in which themetal hydride and/or reversible metal hydride former is suspended. An“inert liquid” includes a liquid that does not chemically react eitherwith H₂ or with the metal hydride and/or reversible metal hydride formerat the temperatures and pressure in which it will be used, and that willnot deactivate the surface of the hydride or hydride former in relationto its catalytic capability to dissociate the H₂ molecule into atoms orto prevent recombination of the atoms into the H₂ molecule. The inertliquid has the capacity to dissolve measurable amounts of hydrogen.

The carrier liquid in some examples is an organic carrier liquid, suchas mineral oil or a low molecular weight hydrocarbon, for example, analkane (e.g., pentane or hexane). Other carrier liquids could includefluorinated hydrocarbons, such as perfluorodecane, silicone basedsolvents, saturated organic liquids, such as undecane, iso-octane,octane and cyclohexane, or mixtures of high boiling point hydrocarbonssuch as kerosene, and mixtures of them.

In some examples, the inert carrier liquid is a non-toxic light mineraloil that exhibits a high flash point, in the range of about 154° C. toabout 177° C. and a viscosity in the range of about 42 Saybolt Universalseconds (S.U.s.) to about 59 S.U.s. The mineral oil is not chemicallyreactive with metal hydrides, produces relatively low vapor pressure,and remains liquid through a temperature range of about −40° C. to 200°C. The carrier liquid renders the slurry pumpable and, as a safe liquid,simple to store or transport. The carrier can act as a barrier betweenthe hydride and atmospheric water, reducing the reaction of the two toform a hydroxide, which can reduce the ability of the slurry to storeand release hydrogen. The use of a slurry permits easy refueling, as bytopping off a tank. Other carriers may work well, including carriersthat are without water bonds and preferably are without OH bonds.Silicone-based carriers may also work for slurries.

In some cases, the slurry includes a dispersant. The dispersant can be,for example, a triglyceride dispersant, which sterically stabilizes theslurry. The triglyceride dispersant can be, for example, triglyceride ofoleic acid, or triolein. Other dispersants that could be used includepolymeric dispersants, e.g., Hypermer™ LP1. The dispersant can bepolymeric dispersant. A combination of triglyceride and polymericdispersant can also be used and may be particularly useful if thehydride is magnesium hydride. Other dispersants include oleic acid,polyacrylic acid, and hexadecyltrimethylammonium bromide (CTAB). Thedispersant can in some cases be present at concentrations of at leastabout 0.05% (e.g., at least about 0.1%, at least about 0.5%, at leastabout 0.75%, at least about 1.0%, at least about 1.5%, at least about2.0%, at least about 2.5%, at least about 3.0%, or at least about 3.5%)and/or at most about 4.0% (e.g., at most about 3.5%, at most about 3.0%,at most about 2.5%, at most about 2.0%, at most about 1.5%, at mostabout 1.0%, at most about 0.75%, at most about 0.5%, or at most about0.1%). For example, a blend including magnesium hydride, light mineraloil, and a mixture of 0.0625% CTAB with 1% poly(acrylic) acid forms astable slurry. The CTAB makes the slurry more flowable and thepoly(acrylic) acid helps to keep the magnesium hydride particles insuspension. One function of the dispersant is to attach to the particlesof hydride, increasing the drag of the particle in the carrier fluidthus helping to prevent settling. The dispersant also helps to keep theparticles from agglomerating. The dispersant promotes the formation ofthe slurry and the stabilization of the hydride into the mineral oil.Dispersants can in certain embodiments also have surfactant propertiesthat may also be useful in the formation of the slurry.

The metal hydride is typically a reversible metal hydride, e.g., areversible metal or metal alloy hydride. A reversible hydride former,e.g., a reversible metal hydride former, is anything (e.g., any metal oralloy) that is capable of reacting with hydrogen reversibly to form ahydride (i.e., that is capable of reversibly going from hydride form tonon-hydride form, generally depending on conditions to which the slurryis subject). The reaction, in a simple form, involves bringing gaseoushydrogen in contact with the hydride former. In the case of a metalhydride former, this reaction can be represented as follows:

M+x/2H₂←→MH_(x)

where M is the metal hydride former and X is the number of hydrogenatoms in the final hydride product. This reaction is sometimes describedas an adsorption process rather than a bonding process.

The reaction direction is determined by the pressure of the hydrogen gasand/or the temperature of the reaction. In some examples in whichmagnesium hydride is utilized, a temperature of from about 250° C. toabout 400° C. (e.g., from about 280° C. to about 350° C. or from about290° C. to about 320° C.) is required for the hydriding of the metal,while a temperature of from about 280° C. to about 400° C. (e.g., fromabout 300° C. to about 380° C., from about 320° C. to about 360° C., orfrom about 310° C. to about 340° C.) results in dehydriding of themetal. Other hydrides can operate with significantly reducedtemperatures and pressures, e.g., absorption and desorption temperaturesof no more than about 250° C. (e.g., no more than about 225° C., no morethan about 200° C., no more than about 175° C., no more than about 150°C., no more than about 125° C., no more than about 100° C., or no morethan about 80° C.). In certain embodiments, alloys and/or mixtures ofhydrides may improve both the kinetics and the temperature ranges ofuse. Examples of such are provided below. Generally, for the hydridingof the metal, an increase in the hydrogen pressure results in a fasterhydriding reaction and/or a lower temperature requirement for hydriding.In some cases, the hydrogen pressure is at least about 15 psia (e.g., atleast about 50 psia, at least about 100 psia, at least about 150 psia,at least about 200 psia, or at least about 250 psia) and/or at mostabout 300 psia (e.g., at most about 250 psia, at most about 200 psia, atmost about 150 psia, at most about 100 psia, or at most about 50 psia).The pressure will generally be partially dependent upon the temperature(and vice-versa). For example, while magnesium hydride slurries producea relatively rapid absorption of hydrogen at 300° C. at a pressure of150 psia, a lower temperature might provide a faster reaction.

Generally, a fast reaction is desirable to reduce costs. Duringabsorption, however, heat is produced and must be removed from thesystem. High rates of heat release could potentially decompose the oilin the slurry. In certain embodiments, a combination of temperature andpressure parameters can be used to control the direction and speed ofthe reaction, and thus the heat produced. For example, the pressure canbe initially relatively low, and can then be increased as the processproceeds.

As the hydride reaction is reversible, a slurry of a hydride former canfunction to transport energy in the form of hydrogen repeatedly, beingcharged and discharged many times (e.g., at least about 5 times, atleast about 10 times, at least about 20 times, at least about 25 times,at least about 50 times, at least about 75 times, at least about 100times, at least about 125 times, at least about 150 times, at leastabout 250 times, at least about 500 times, at least about 1000 times, orat least about 2000 times). Generally, the greater the number ofcharge/discharge cycles, the more cost-effective the system. Forexample, at large scale, a chemical hydride slurry used in anon-reversible fashion (e.g., in which the hydrogen is evolved by mixinga metal hydride with water to form hydrogen and a metal hydroxide; suchare disclosed in, for example, U.S. application Ser. No. 10/044,813,titled Storage, Generation, and Use of hydrogen, filed on Nov. 14, 2002,and incorporated herein by reference) should be able to deliver hydrogenat a cost of about $4/kg of hydrogen. If a reversible magnesium hydrideslurry carried only half as much hydrogen at the delivery point, thecost of hydrogen for a single use would be about $8/kg of hydrogen. Ifthe reversible magnesium hydride slurry can be cycled 100 times,however, the cost of the hydrogen will drop to approximately the cost ofthe hydrogen used in the slurry and the cost of the transportation ofthe slurry (e.g., $1.65+$0.10+$8/100=$1.83/kg). Any reuse of the hydrideslurry in a reversible system will reduce the cost of the hydrogen. Incertain examples, a limiting factor on the number of times the slurrycan be charged and discharged is the slow formation of the oxide orhydroxide form of the chemical hydride former, e.g., due to exposure toatmospheric moisture or air. Another issue that might limit the life ofa metal hydride slurry might be damage to the oils and dispersants.These issues can influence how often the hydride slurry must return tothe factory to be recycled. To recycle the hydride slurry, the oils arefirst separated from the solids. Then the solids are reformed to puremetals. Then the metals are alloyed to form fresh hydride former and thefresh hydride former is reacted with hydrogen to form fresh hydrideslurry.

Generally, any reversible hydride former would be suitable, includingmetal and/or metal alloy hydride formers, such as, for example,magnesium, vanadium, FeTi, CaNi₅, MgNi₂, NaAl or other metal hydrideformers whether an elemental metal, metal alloy or intermetallicmaterial. Intermetallic hydride formers include LaNi_(4.5) Al_(0.5),LaNi₅ and TiFe_(0.7) Mn_(0.2). Metallic hydride formers include thetransition metals (periodic table Groups IIIA to VIIIA), including thelanthanide and actinide series. They have a large capacity for hydrogenstorage coupled with ready release of hydrogen at moderate temperaturesand pressures and an ability to undergo many cycles of absorption anddesorption with little decrease in capacity.

Metals and metal alloys known to form reversible hydrides for reversiblycapturing hydrogen include titanium alloys as set forth in U.S. Pat. No.4,075,312, lanthanum alloys as disclosed in U.S. Pat. No. 4,142,300, andother alloys as shown in U.S. Pat. No. 4,200,623. Elemental metals knownto form metal hydrides are described in “Metal Hydrides” by W. M.Mueller, J. P. Blackledge and G. G. Libowitz, Academic Press, N.Y. 1968.These patents and references are incorporated here by reference.

The slurry is initially formed by adding a reversible hydride former andoptionally a dispersant to a carrier liquid. The reversible hydrideformer is generally finely ground before being mixed with the othercomponents of the slurry. In some cases, the reversible hydride formerpowder is first combined with a mixture of the mineral oil anddispersant, which is then ground (e.g., in a grinder or mill) to furtherreduce the size of the particles. In some cases, the final particles areprimarily from about 1 microns to about 200 microns (e.g., from about 1microns to about 100 microns or from about 1 micron to about 50 microns)in size across their smallest dimension. In some cases, a small amountof hydride (e.g., a hydride that includes the same reversible hydrideformer being added to the slurry) is added to the slurry prior tocharging the slurry. The amount of hydride added to the hydride formerin some embodiments is from about 1% to about 50% (e.g., from about 3%to about 20%). The most cost effective range will typically depend onthe reaction rate and the cost of the hydride former. For magnesiumhydride, the hydride can function as a catalyst, increasing the rate ofhydride formation by the reversible hydride former, for example, asdescribed in U.S. Pat. No. 5,198,207, incorporated herein by reference.In some cases, such as when the depleted slurry is one that had beencharged and had since been discharged, it has been hypothesized thatsome of the hydride remains in hydride form and provides the catalystfunction without the need for the addition of a chemical hydride as acatalyst.

Examples of the slurries can have a liquid-like flow characteristic thatcan allow for the use of existing liquid fuel infrastructure in thestorage and transportation of the slurry. The nature of the carrierliquid, the amount of the dispersant, and the size of the hydrideparticles all affect the viscosity of the slurry. The oil in the slurrycan protect the hydride from unintentional contact with moisture in theair. The slurry can serve as a path for the dissipation of heatgenerated from the exothermic charging reaction. The dispersantmaintains the hydride particles in suspension. The dispersant attachesto the particles and fends off adjacent particles to preventagglomeration of the particles.

The slurry burns only if high heat is applied, as by a blow torch, andmaintained. Upon removal of heat, the burning of the slurry ceases andflames die out.

The slurry is generally capable of holding between about 3% and about 6%by weight of hydrogen. The slurry in some embodiments can absorb up to100% of the theoretical amount of hydrogen that can be absorbed. Theslurry in certain embodiments can release from about 70% to about 98% ofthe uptaken hydrogen (e.g., from about 80 to 98% or from 90 to 98% ofthe uptaken hydrogen). The residual hydride that remains can thenfunction as a catalyst for the recharging of the slurry.

The charging device includes a slurry-holding vessel and a heatingdevice (e.g., heating coils, a heat exchanger, a heating plug, and/or acounter flow heat exchanger) for heating the slurry therein to thecharging temperature. The charging device also includes a hydrogen gasinlet and optionally a pressure regulator for maintaining the chargingpressure within the vessel. As the charging reaction is exothermic, thecharging device may include a heat removal apparatus (e.g., a heat pump,heat exchanger, and or a plug) for maintaining the slurry being chargedwithin a desired temperature range. The charging device can also includestirring or mixing components to create a more uniform temperaturedistribution throughout the slurry and to assist in the distribution ofhydrogen throughout the slurry.

The charging device can be supplied with freshly created slurry,depleted slurry or a combination of the two.

In some examples, such as in FIG. 1, the charging device operates on abatch-by-batch basis. Depleted slurry is pumped into the device, whichis heated and supplied with hydrogen gas until the slurry is charged.The pressure is vented, the slurry is cooled, and the slurry is pumpedfrom the device (e.g., to a storage tank). The process is then repeated.

In other implementations, the charging device operates continuously asslurry is continuously pumped, heated, charged, cooled and removed.

As shown in FIG. 2, in a continuous-mode charging apparatus 150,depleted metal hydride slurry 152 is fed by a pump 154 into a firstsection of tubing 156, where it is heated to the charging temperature byheating coils 158. Once heated, the depleted metal hydride is pumpedinto a pressure chamber 160 having a headspace 161 located above theslurry 152. Hydrogen gas 162 is introduced via gas inlets 163 into theheadspace 161, where it is in direct contact with a surface 153 of theslurry 152. The hydrogen gas 162 is introduced under pressuresufficient, given the temperature selected, to initiate the hydridereaction. The pressure chamber 160 is of a length l sufficient, whencombined with the flow rate of the slurry, to result in a lag time ofthe slurry in the pressure chamber 160 sufficient for substantiallycomplete charging of the slurry. As the metal in the depleted metalhydride slurry 152 is hydrided to form a charged metal hydride slurry168, heat is given off by the slurry. An optional heat exchanger 166collects and transfers heat from the slurry to the first section oftubing 156, where it assists in the heating of the depleted metalhydride slurry. Once the slurry is fully charged, it exits the pressurechamber 160 and enters a third section of tubing 172, in which it iscooled to about room temperature, e.g., by the heat exchanger 166. Thecharged metal hydride slurry is then pumped out of the charging device150.

In a variation of this arrangement, the process could be started bypumping some discharged slurry through a counter flow heat exchanger andthen through a heater (that would raise the temperature of thedischarged slurry to operating temperature until there is enough heatfrom the charged slurry leaving the charging section) and then into thecharging volume where hydrogen will contact the slurry. A reactionbetween the depleted hydride and the hydrogen will produce heat, some ofwhich must be removed actively to maintain the slurry temperature at thedesired reaction temperature. After being in the hydriding section for acouple hours, the hydriding should be complete and the charged hydrideslurry will pass back through the counter flow heat exchanger and into aseparate container for the charged slurry. The hot slurry passingthrough one side of the counter flow heat exchanger will lose its heatto the cold depleted slurry passing through the other side of thecounter flow heat exchanger.

Generally, the discharge device is similar to the charging device. Thedischarge device generally includes a fluid-holding vessel and a heatingdevice (e.g., heating coils, a heat exchanger, and/or a heating plug)for heating the slurry therein to the discharging temperature. Wheremagnesium hydride is utilized, the discharging temperature can be atleast about 280° C. (e.g., at least about 300° C., at least about 320°C., at least 340° C., at least about 350° C., at least about 360° C., atleast about 370° C., at least about 380° C., or at least about 390° C.)and/or at most about 400° C. (e.g., at most about 390° C., at most about380° C., at most about 370° C., at most about 360° C., at most about350° C., at most about 340° C., at most about 320° C., or at most about300° C.). Other hydrides can operate with reduced temperatures andpressures. The device further includes a hydrogen gas outlet forreleasing hydrogen gas from the vessel. The discharge device optionallyfurther includes a heat removal apparatus (e.g., a heat pump, heatexchanger, or an insulated counter flow heat exchanger) for reducing thetemperature of the slurry once it is depleted of releasable hydrogen.

In some examples, such as in FIG. 1, the discharge device operates on abatch-by-batch basis. Charged slurry is pumped into the device andheated, at which time hydrogen evolves from the slurry. The depletedslurry is then optionally cooled and pumped from the device (e.g., to astorage tank). The process is then repeated.

In some examples, charged slurry is continuously pumped into thedischarge device, heated, depleted, cooled and removed. FIG. 3illustrates an example of a continuous-mode discharge device 200, inwhich charged metal hydride slurry 202 is fed by a pump 204 into a firstsection of tubing 206, where it is heated to the desorption temperatureusing heating coils 208. Once heated, the charged metal hydride slurry202 passes into a desorption chamber 210 having a headspace 211 above asurface 203 of the slurry 202. Hydrogen gas 212 desorbs from the chargedslurry 202 into the headspace 211, from which it is vented via gasoutlets 212. A pressure valve 214 can be used to control the pressurewithin headspace 211. The length l′ of the desorption chamber 210 tubingis sufficient, when taken in combination with the flow rate of theslurry, to permit substantially all of the available hydrogen to desorb.The slurry, which is now a depleted metal hydride slurry 216, exits thedesorption chamber 210 and enters a third section of tubing 220, inwhich it is cooled to about room temperature, optionally by means of aheat exchanger 222 which takes the heat from the depleted metal hydrideslurry 216 and applies it to the charged metal hydride slurry 202entering the discharge device 200. The depleted metal hydride slurry 216is then pumped out of the discharge device 200, e.g., for storage and/ortransport.

The pressure valve 214 can in some cases be coupled to a cooling system226 to cool the hydrogen gas 212 and to condense any oils 228 which hadvolatilized and vented along with the hydrogen gas 212. Any oil 228 socondensed could be added back into the depleted metal hydride slurry216. The hydrogen gas 212 can in some cases be run through a filter 230,e.g., a charcoal filter, to remove any remaining oils or otherimpurities. The now purified hydrogen gas 212′ can then be fed tofurther processing, such as, for example, bottling. Alternatively, thehydrogen gas 212′ can be supplied to a hydrogen-consuming process suchas a fuel cell or a welding system.

Generally, a first energy source is used to form or extract the hydrogenthat is stored in the hydride slurry. The first energy source is incertain examples an energy source that is readily available at aparticular location (e.g., a first location) and/or is not readilyavailable at, and/or not readily transferable to, a second location.Such energy sources include renewable energy sources such as, e.g.,wind, geothermal, hydroelectric, ocean power (e.g., drawing on theenergy of ocean waves, tides, or on the thermal energy stored in theocean), biomass, and solar energy in the form of heat or electricity.Such energy sources generally do not produce greenhouse gases and arenot subject to depletion. Biomass can produce greenhouse gases, buttypically does not contribute substantial amounts of additionalgreenhouse gases to the atmosphere, since the biomass uses thegreenhouse gases to make itself. In some embodiments, nuclear energy canbe utilized to produce hydrogen. In other embodiments, fuels generallyutilized as energy sources (e.g., coal, oil, and/or natural gas) can beutilized to produce hydrogen. The hydrogen can be produced at a smallnumber of locations, where care can be taken to reduce pollutionresulting from the burning of such fuels.

Many of these energy sources are not themselves easily transportable inan unused and/or stable form, in contrast to fossil fuels. In addition,many of these energy sources are in locations in which the energy demandis low (e.g., areas of low population density and/or littleindustrialization). For example, as illustrated in FIG. 1, the firstlocation 12, Kansas, has an abundance of wind energy available, butlittle demand for energy as compared with other parts of the country. Insome locations, the available energy is greater than the energy demand.This excess energy can be stored and transported to locations of higherenergy demand.

Example 1

A mixture of 50 wt % magnesium hydride and Paratherm NF heat transferoil was placed in a Parr autoclave, where it was subjected to thefollowing experimental conditions. A plot of both temperature andpressure of the autoclave as a function of time is found at FIG. 4.

The autoclave was purged with hydrogen five times at a pressure of 150psia to reduce the oxygen content of the gas in the vessel to no morethan about 2 ppm. The pressure in the vessel was reduced to atmosphericpressure after each pressurization and after final pressurization. Thevessel was heated to 140° C., a temperature at which any water in theoil would have reacted with the magnesium hydride to form hydrogen. Theresulting pressure rise would have caused the produced hydrogen to leavethe vessel and be collected in an inverted bottle filled with water; nobubbles were observed, indicating that no water was present in the oil.

The vessel was heated to 370° C., a temperature at which hydrogendesorbs from magnesium hydride, and hydrogen was seen to evolve for aperiod of about 2 hours, during which time about 80% of the hydrogentheoretically bound in the magnesium hydride was evolved. The hydrogenevolved was measured in an inverted bottle that displaced water in thebottle.

The autoclave was then pressurized with hydrogen gas at 150 psia, whilethe temperature was held at about 370° C. The pressure dropped only afew psi over the course of 1.4 hours, indicating that little hydrogenwas absorbed by the slurry. The temperature was then reduced to about320° C. At this temperature hydrogen was readily absorbed (i.e., wasreadily incorporated into magnesium hydride). The system was held atthis condition for 1.5 hours, with one additional hydrogenpressurization, and was then cooled.

As can be seen in the graph of FIG. 4, when initially heated to about370° C., the slurry did not evolve hydrogen (indicated by the pressureof nearly 0 psia). A set amount of hydrogen was introduced, indicated bythe increase in pressure to about 150 psia at about 10000 seconds. Atthis temperature and pressure, the slurry did not absorb the hydrogen(indicated by the pressure remaining at about 150 psia over time). Oncethe temperature was reduced to the absorption temperature of about 320°C., the pressure fell, indicating that hydrogen was being absorbed bythe slurry. The rate of the pressure drop increased over time. This isbelieved to be a function of the initially-formed magnesium hydrideacting as a catalyst, speeding the hydride reaction and utilizing thehydrogen at a more rapid pace. Upon adding more hydrogen to the system(indicated by the spike in pressure at about 18000 seconds), the rate orpressure drop (indicative of the rate of hydrogen uptake) increasedagain, tailing off only as the temperature was reduced at the end of theexperiment.

While embodiments described above refer generally to forming hydrogen ator near the site of metal hydride formation or charging, hydrogen canitself be stored and transported to metal hydride charging sites. Forinstance, hydrogen can be transported from large scale steam methanereformers to remote markets (e.g., markets several hundred miles away).

Other embodiments are within the scope of the following claims.

What is claimed is:
 1. A method, comprising: releasing hydrogen fromwater at a first location using energy from a first energy source;storing the released hydrogen in a metal hydride slurry; andtransporting the metal hydride slurry to a second location remote fromthe first location.
 2. The method of claim 1, further comprisingreleasing the hydrogen from the metal hydride slurry to form hydrogenand a metal hydride slurry that is at least partially depleted.
 3. Themethod of claim 2, further comprising transporting the partiallydepleted metal hydride slurry from the second location to the firstlocation.
 4. The method of claim 3, further comprising recharging thedepleted metal hydride slurry by releasing energy from water at thefirst location using energy from the first energy source, and storingthe released hydrogen in the depleted metal hydride slurry to form themetal hydride slurry.
 5. The method of claim 4, further comprisingrecharging the depleted metal hydride slurry and releasing hydrogen fromthe metal hydride slurry for at least 50 cycles.
 6. The method of claim2, further comprising utilizing the hydrogen released from the metalhydride slurry as an energy source.
 7. The method of claim 1, whereinthe first energy source comprises a renewable energy source.
 8. Themethod of claim 1, wherein the released hydrogen is stored in a metalhydride slurry at the first location.
 9. The method of claim 1, whereinthe first location has a first energy demand, the second location has asecond energy demand, and the first energy demand is lower than thesecond energy demand.
 10. The method of claim 1, wherein the metalhydride slurry is transported via a carrier selected from the groupconsisting of a rail car, a truck, a tanker, a pipe, a barge, and anycombination of these.
 11. The method of claim 1, wherein the metalhydride slurry comprises magnesium, magnesium hydride, mineral oil and adispersant.
 12. A system, comprising: an electrolyzer to extracthydrogen from water using energy from a first energy source at a firstlocation; a charging device coupled to electrolyzer, the charging devicecomprising a slurry inlet, a slurry outlet, and a heating device capableof heating a slurry in the charging device to at least about 320° C. 13.The system of claim 12, wherein the system is capable of maintaining apressure in the charging device of at least about 150 psia.
 14. Thesystem of claim 12, the charging device further comprising a pump topump a slurry from the charging device through the slurry outlet. 15.The system of claim 12, the charging device further comprising aregulator to maintain a temperature of a slurry contained in thecharging device at no more than about 350° C.
 16. The system of claim12, further comprising a storage container coupled to the chargingdevice slurry outlet.
 17. The system of claim 12, further comprising adischarge device comprising a heating device capable of heating ahydride slurry contained in the discharge device to at least about 370°C.
 18. A system, comprising: a first device to produce hydrogen usingelectricity from a first energy source; a metal hydride slurry chargingdevice coupled to the first device; a metal hydride slurry storagevessel coupled to the metal hydride slurry charging device; and a pumpto pump a slurry from the metal hydride slurry charging device to themetal hydride slurry storage vessel.
 19. The system of claim 18, whereinthe first device comprises an electrolyzer.
 20. The system of claim 18further comprising a pump coupled to the storage vessel to transfer aslurry from the metal hydride slurry storage vessel to a slurry carrier,wherein the slurry carrier is selected from the group consisting of atruck, a boat, a rail car, a barge, a pipe, and any combination ofthese.